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Elevated CO on burner tune up

Robert_H
Robert_H Member Posts: 140
I haven't been on the wall for years since I replaced my heating system. Now I'm probably one of the oldest HVAC apprentices around and need some advice.

I was servicing a Weil Mclain SCO-4 in an old house that was recently purchased and is not yet occupied. The boiler looks to be in good shape and the smoke pipe/draft regulator are solid as well. The pipe and heat exchanger both had a thin coating of soot.
The label called for called for 1.25 80B for the becket burner and 100PSI pump pressure. I did not have a 1.25 and the local supply house was picked pretty clean. I used a .90 80B and planned to raise the pump pressure to 150 to get 1.10 GPH. Which doesn't seem overly underfired. Maybe I'm wrong on that. When I checked the pump pressure it was already set to 150. Thinking back now, I believe the old nozzle was a 1.00 80B. After a good scrubbing and new Filter/strainer and nozzle I fired the boiler off and adjusted the shutter for a good visual flame and checked the draft.
After ten minutes I checked smoke starting at 3 and set to a trace. Then, with the analyzer in the pipe, I adjusted to 12 CO2 and verified zero smoke.
draft over the fire was .01
Stack temp 445
amb temp 48
o2 4.8
co2 12.10
eff 83.6
ex air 27.7
co 27

I left the analyzer on while I was cleaning up and noticed that over time the CO was gradually increasing and eventually got to 210.
Could this amount of under firing cause the CO level? anything else I should be looking at?
The combustion chamber is in good shape and all the refractory pieces are in place.
I plan to return and put the proper nozzle in and get the correct firing rate, reset smoke, test and get the CO under control.

Thanks
Robert

Comments

  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    edited February 5
    Yes, incomplete combustion/impinging would be my guess. Also, make sure you're doing the smoke test right-slow pull should take 3 seconds, pause 1 second, 3 second to return, pause 1 second. At true zero smoke you'll then need to add air to drop that CO2 1%.
    Double check your nozzle size and angle, make sure you're not impinging.
    Double check over fire draft.
    All reading done at steady state.
    1.00 @ 150 is pretty close to your 1.25 firing rate, if not impinging.
    Also, just might be a bad nozzle.

    steve
    Robert_HSuperTech
  • Jamie Hall
    Jamie Hall Member Posts: 22,878
    Not an oil burner tech. by a long shot -- but a pretty good tuneup guy. I think @STEVEusaPA may have it. If the flame is impinging -- at all -- on the firebox anywhere, you'll have problems, and rising CO could, I expect, be one. Find out what the manufacturer's specified nozzle is (flow rate, pattern, the works) and use that.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Robert_H
  • Robert_H
    Robert_H Member Posts: 140

    Yes, incomplete combustion/impinging would be my guess. Also, make sure you're doing the smoke test right-slow pull should take 3 seconds, pause 1 second, 3 second to return, pause 1 second. At true zero smoke you'll then need to add air to drop that CO2 1%.
    Double check your nozzle size and angle, make sure you're not impinging.
    Double check over fire draft.
    All reading done at steady state.
    1.00 @ 150 is pretty close to your 1.25 firing rate, if not impinging.
    Also, just might be a bad nozzle.

    Thank you Steve, I do take a slow count when smoke testing but I don't pause as you recommend and I will do that.

    By impinging do you mean any contact with the combustion chamber? in this case I do not see that.
    Also what is the full name of your app? that sure beats my current pdf.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,484
    edited February 6
    By impinging do you mean any contact with the combustion chamber? in this case I do not see that.
    .

    Impinging is when a droplet of oil comes in contact with an object before the droplet is completely vaporized. Oil will not burn in the liquid state, so those tiny droplets must evaporate completely. Since the flame is over 2000° those tiny droplets evaporate quickly. However, if some of those droplets hit the cold cast iron (maybe 300° because there is 180° water on the other side of the cast iron) or the combustion chamber. (maybe 600° to 1200° that is reflecting the heat back onto the flame) before the droplet is completely evaporated, then that droplet will not completely burn. Even with extra air, you will not get that oil to completely burn.

    You may have noticed carbon deposits on some end cones or retention heads over the years of oil burner service. That carbon build up is incomplete combustion of. the fuel and the leftover carbon sticking to that colder (compared to the 2000° flame) surface. Then the next droplet does the same thing, and it builds up over time. If you let that go unchecked you can have 6 months of burning OK, then poorly, then all of a sudden the build up carbon catches a greater portion of the fuel and you get the burner to make a #10 smoke and you get a plugged boiler in about 30 minutes of operation. So 6 months… then the last 30 minutes is a disaster.

    On those WM SGO and WGO boilers, it is not easy to see the flame as it exits the burner. But you can see the flame in the chamber and they are usually several inches away from impinging on anything. An incorrect Z dimension on the Beckett burner with the incorrect nozzle spray angle may be impinging at the retention cone.


    And Yes... that is a interesting App Steve. Wish I had it before I retired.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,296
    If you have 12%Co2 and 0 smoke the burner seems like it is doing it's job. Maybe some soot inside was still burning off. Was the boiler up to temp? A cold boiler will give you CO

    If it doesn't straighten out I would experiment with some different nozzles. Do a nozzle application test. Try a hollow with the same gph and spray angle without changing adjustments and see what direction the #s go in. One will be better than the other. One you find out if it likes hollow or solid try different spray angles like a 70 or 60 and see which is better.

    Don't forget the oil pressure will have some effect on the spray angle.

    You didn't mention which burner you have is it a Carlin or Beckett?

    It would not be the first or last time the boiler mfg. nozzle specs prove to be not the best choice.

    Maybe test your analyzer on another boiler where you know the #s it puts out.

    If it was me I would stay around 1.00-1.10 gph.
  • pedmec
    pedmec Member Posts: 907
    Sounds more like your running out of combustion air in the mechanical room. i do mostly gas combustion and when i'm in a confined room my CO will rise over a longer period of run time. There is only so much O2 available for combustion. You don't deplete the existing O2 in a confined room right away. it takes a cycle that lasts longer and longer to notice. Depends on how tight the room and house are to prevent infiltration. impingement would cause a high smoke number
    STEVEusaPAEdTheHeaterManRobert_HAlanWornham
  • PatN
    PatN Member Posts: 19
    Steve could you post a link for your Pump Pressure Calculator
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    edited February 9
    It's only usable on an IOS device for free. It's a FileMaker database file, so you would need to download FileMaker Go (free) on the app store first.
    Then open file from dropbox link, then 'Share', then 'Send copy of file', then select FileMaker Go. You can put a shortcut on your home screen to open directly from there.
    Send me a PM.

    Here's my YouTube channel with instructions on how to put it on your IOS device, and how to use most of the modules.
    You could use it on any desktop, but you have to purchase the FileMaker database program to run it. Not really worth it unless you want to modify the program.


    steve
    ethicalpaulRobert_HSTEAM DOCTOR
  • captainco
    captainco Member Posts: 791
    The slowly rising CO is either oil impingement on the flame cone or residual burn off of oil saturated in the combustion chamber, gut the peak CO at Light-off and Shut-down would help.
    Bad oil nozzles have CO that is above 100ppm from start to finish and yours is fine.
    Can't run an oil burner out of combustion air. They have their own combustion air fan and adding more air to the room is useless.
    Old timers had trouble getting smoke reduced on oil so they changed the standard for smoke testing , pump as slow as you can and as few pumps as possible
    STEVEusaPARobert_H
  • Robert_H
    Robert_H Member Posts: 140

    By impinging do you mean any contact with the combustion chamber? in this case I do not see that.
    .

    Impinging is when a droplet of oil comes in contact with an object before the droplet is completely vaporized. Oil will not burn in the liquid state, so those tiny droplets must evaporate completely. Since the flame is over 2000° those tiny droplets evaporate quickly. However, if some of those droplets hit the cold cast iron (maybe 300° because there is 180° water on the other side of the cast iron) or the combustion chamber. (maybe 600° to 1200° that is reflecting the heat back onto the flame) before the droplet is completely evaporated, then that droplet will not completely burn. Even with extra air, you will not get that oil to completely burn.

    You may have noticed carbon deposits on some end cones or retention heads over the years of oil burner service. That carbon build up is incomplete combustion of. the fuel and the leftover carbon sticking to that colder (compared to the 2000° flame) surface. Then the next droplet does the same thing, and it builds up over time. If you let that go unchecked you can have 6 months of burning OK, then poorly, then all of a sudden the build up carbon catches a greater portion of the fuel and you get the burner to make a #10 smoke and you get a plugged boiler in about 30 minutes of operation. So 6 months… then the last 30 minutes is a disaster..
    Thank you very much, so if I understand right, "impingement" is not necessarily something you can see even if you could see the entire flame. but something I should assume might be happening if I have high CO and evaluate for it along with the other possible causes. I did find crud on the retention head and scrubbed it clean.

    If I go back and find the retention head wet with oil, would that indicate impingement?
    Thank you again
    Robert

  • Robert_H
    Robert_H Member Posts: 140

    If you have 12%Co2 and 0 smoke the burner seems like it is doing it's job. Maybe some soot inside was still burning off. Was the boiler up to temp? A cold boiler will give you CO

    You didn't mention which burner you have is it a Carlin or Beckett?

    It would not be the first or last time the boiler mfg. nozzle specs prove to be not the best choice.

    Maybe test your analyzer on another boiler where you know the #s it puts out..

    The boiler had ran for about ten min when I started testing and I was with it for a good 45 min. it was starting to shut off on pressure.

    It is a Beckett

    I did check the CA on friends boiler that I service and my gas modcon.
    Thank you!
  • Grallert
    Grallert Member Posts: 633
    Sometime a bad pump shaft seal will cause this as well. Hard to diagnose but a wetness around the shaft or a little oil trial will show.
    Miss Hall's School service mechanic, greenhouse manager,teacher and dog walker
    Robert_H
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,484
    Robert_H said:

    Thank you very much, so if I understand right, "impingement" is not necessarily something you can see even if you could see the entire flame. but something I should assume might be happening if I have high CO and evaluate for it along with the other possible causes. I did find crud on the retention head and scrubbed it clean.

    If I go back and find the retention head wet with oil, would that indicate impingement?
    Thank you again
    Robert

    You will see the results of impingement. If a piece of the combustion chamber were to flake off and hang in the path of the nozzle spray, there will be a carbon build up resulting from that impingement. If the nozzle has a defect from being contaminated(common) or factory defect(rare), then an uneven spray pattern may squirt at a specific spot in the chamber leaving a black or dark gray impression at that location. Sometimes after-drip will leave wet oil on the end cone or retention ring. That will evaporate and leave carbon or a varnish like coating behind. If that builds up over time enough to cause a small carbon mountain to form and get in the way of the oil spray, Then impingement will happen in 6 months from now (or 6 years from now) and make a carbon doughnut hanging off the end cone, in a matter of 10 minutes. And you will never see it unless you look down the burner air tube with a flashlight before you put the nozzle assembly back in place.

    That is one habit I formed when doing oil burner service. Even if I just cleaned the end cone on a burner that is on a swing open door so you can see the firing side of the end cone, When I put it all back together, I look down at the end cone from the opening where you replace the nozzle assembly (usually where you open the door that is holding the ignition transformer) to see that nothing is blocking the airflow or oil pattern. It is just something that I can't help doing… start to insert the nozzle assembly… pause… get the flashlight… look at the end cone… install the nozzle assembly. It’s a great habit to get into.


    If I go back and find the retention head wet with oil, would that indicate impingement?
    Not necessarily. The whole flame retention thing is based on that area around the slots in the end cone or retention ring that are causing a low pressure area that will cause the air that is driving the oil droplets into the chamber to be burned, will also cause some of those droplets to follow the higher pressure air to turn around and find that low pressure zone to make it look like the flame is actually burning on the metal ring.

    What is actually happening is that low pressure area is actually about 3/32" away from the metal and the flame is really burning 1/8" away from the metal. The cold air from the boiler room (the combustion air) is keeping the metal with the slots cool enough so that it doesn't over heat, turn cherry red, then melt away. If you are finding the cone or ring with the slots wet, that is probably after drip from the burner shutting off, and the 100PSI (or higher) oil just leaving the nozzle and not burning.

    BTU. It may be impingement if the Z dimension on a Beckett with an F type head or a retention ring is not properly fitted to the nozzle assembly so the spray is hitting the metal parts before it gets into the air flow of the combustion air. The amount of oil on the end cone and any that drips into the air tube will tell the difference between after drip and impingement.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    Robert_H
  • Robert_H
    Robert_H Member Posts: 140
    Follow up
    I went back yesterday and ran combustion analysis again. The CO climbed to 52 ppm and stayed there. The house is unoccupied so the owner had the thermostat at 50f. Seems like the problem was left over soot burning as a few people mentioned and it just needed time to burn off. Thinking atmosphere in the combustion chamber might have changed, from when I set it last week, I rechecked draft, set smoke and co2. Ill be back in that area in a week and will see if the CO drops any more.

    I really appreciate everyone taking the time to help me out!
    Robert
    EdTheHeaterMan